Just been looking at the instrument panel illumination in RAVE (E2, page 4 on my copy).
As far as I can see power / signal for the panel illumination comes from BECM signal on terminal 7, connector C258 of the BECM. That then splits 2 ways at splice S205 and goes to terminals 4 and 14 on the instrument cluster. 4 feeds the message centre, 14 goes, via various routings, to the 6 panel bulbs, in 2 sets of 3 (presumably for redundancy, you should only lose half at a time).
Then the panel lights all earth, via connectors 7 and 17 on the cluster to earth point E254. So if you have lost all panel lights I think you need to check earthing point E254 (or the wires to there from both 7 and 17), or the feed in at 14 from splice 205 for loss of power.
Unless I am reading those diagrams completely wrong. I may be as I can't figure out how the dimmer affects it all unless it signals the BECM to vary the feed in to the whole set up. In which case that is somewhere else in the wiring but means you could be looking in the wrong place all this time? If the BECM varies the feed according to the dimmer signal, and it thinks (due to a short / open) that the dimmer is set to off, it is all doing exactly what the signals to it say it should?
RAVE J1, page 1, Dimmer switch says illumination level is stored by the BECM, so it looks like that is the source of your woes. Signal to there being faulty somehow.
RAVE J1 page 6 - dimmer feeds to earth from 2 terminals on BECM. Connector C256, earthing terminal 4 brightens the panel lights, earthing 12 dims them.